Mobile data transmission and data services are constantly making progress. With the increasing penetration of such services, a need for increased bandwidth for conveying the data is emerging. In hitherto known scenarios, networks operated on reserved bands (licensed bands) within the available spectrum, which were reserved for the particular network. As licensed band operation has been increasingly utilized, portions of the radio spectrum that remain available have become limited. Thus, operators, service providers, communication device manufacturers, and communication system manufacturers, are all seeking efficient solutions to utilize unlicensed shared band operation. Communication on an unlicensed shared band is generally based on sharing an available channel between different communication devices. The different communication devices may utilize a common radio access technology RAT. However, in certain scenarios, the different communication devices may utilize different RATs. In an unlicensed shared band, channel access can be distributed, where communication devices can detect a channel, and utilize a channel reservation scheme known to other communication devices in order to reserve a right to access the channel. In distributed channel access, a transmitting communication device and a receiving communication device are generally not synchronized to a global reference.
Currently, a system known as Long Term Evolution LTE is being further developed. When the LTE system concept is further extended in a way that it can be deployed also on unlicensed bands, the devices and local access points have potentially more spectrum available. That spectrum is to be used opportunistically as explained above. This setting can be considered as a kind of non-contiguous carrier aggregation, in which unlicensed spectrum is used as resources or “ground” for secondary carriers/cells for the licensed spectrum primary and secondary carriers/cells, controlled by the network transceiver station (or access node) known as Evolved Node_B, eNB. One step further would be to deploy an eNB totally on some shared band, like in television white space TVWS or in the industrial, scientific and medical, ISM band without any anchor in licensed spectrum (in EUTRAN level) (Evolved Universal Terrestrial Radio Access Network) similar to WLAN deployments to make LTE a competing solution against widely adopted IEEE technologies.
As a future LTE-A system may be deployed on unlicensed bands (e.g. TVWS or ISM bands), for example via carrier aggregation methods as mentioned above, the environment of the spectrum sets further requirements/challenges for the system to operate appropriately. One problem in case downlink carrier aggregation is conducted with one or more component carriers (CC) on unlicensed bands, is to specify certain CC(s) to carry the control/scheduling information (on a control channel such as PDCCH) for a terminal such as a user equipment UE device reliably and without service interruptions due to different interference situation of different CCs at local point of view. Also, in UE point of view, the experienced interference situation may be quite different from eNB side due to interference caused by an unknown system (operating in the same unlicensed band). It could be envisioned also that on unlicensed spectrum deployments with carrier aggregation methods, the cross-carrier scheduling option is to be used to improve interference management and protection of crucial control information transmission among eNBs. Furthermore, there may be some regulatory needs for, e.g., periodic sensing/measurements of the channel on unlicensed/shared band. As an example, for 5 GHz ISM band in Europe, there's tight requirement of sensing radar operations.
Carrier aggregation concept with cross-carrier scheduling method for LTE Rel-10 is currently discussed. In current concepts, the cross-carrier scheduling method is UE specific and component carrier specific and is configured via radio resource control RRC signaling.
In LTE, the channel quality indicator CQI reports are to assist an evolved Node_B, eNB, in selecting an appropriate modulation and coding scheme MCS to use for downlink transmissions. It should be noted that the reported CQI is not a direct indication of signal to interference noise ratio SINR but instead, the UE reports the highest MCS that it can decode with a certain block error rate probability. It is also very questionable whether it is possible to recognize interference coming from other system transmissions with CQI feedback since the bad signal quality may be caused by fading channel.
Furthermore in LTE, the serving eNB may configure and request an individual active UE to perform certain RRM measurement and reporting, specified as a dedicated RRC signaling procedure. Furthermore, in-band dynamic channel quality indication from UE, measured on a physical resource block basis in the DL, and sending sounding signals by UE in the UL are also adopted. On shared bands it is also important to carry out sensing/measurements for unknown interference caused by other system utilizing the same spectrum. In LTE system, protection of, e.g., control information carried by certain CC or by all CCs for themselves is crucial for the system to work reliably.
Thus, there is still a need to further improve such systems in terms of proper interference measurements and reports being enabled.